The invention relates to a diamond-like nanocomposite (DLN) composition having improved (lower) friction properties combined or not with improved (higher) hardness. The invention deals also with an improved process for covering substrates with a layer or film of such a composition in a modified plasma assisted chemical vapour deposition (PACVD) process in vacuum.
Diamond-like nanocomposite (DLN) materials are related or similar to diamond-like carbon (DLC). DLC films (a-C:H, a-C, i-C) display a good combination of high hardness and elasticity, high wear resistance and a low coefficient of friction. Furthermore, because of their chemical inertness, low surface energy and intrinsic smoothness, these films give access to appealing industrial applications such as hard, self-lubricating films, eg. for protection of magnetic discs and media, sliding parts in motors, space applications, optical components etc. However, deposited DLC films exhibit much higher internal stresses (above 1 GPa) than DLN films (200-400 MPa), thus impeding good adhesion to the substrate. DLC films on substrates may thus require the use of intermediate adhesion promoting layers which is not needed for DLN. Another disadvantage of DLC impeding fast commercialisation is the fact that the coefficient of friction of DLC in air increases up to about 0.2 to 0.3 when the relative humidity rises above 50%.
DLN and methods for its deposition on substrates, such as glass, metal or Si-wafers are described in U.S. Pat. Nos. 5,352,493 and 5,466,431. By using the deposition processes disclosed in this patent, diamond-like nanocomposites are produced which consist of an (amorphous)a-C:H diamond-like network and an (amorphous)a-Si:O glass-like network. These networks interpenetrate into each other and some Si-C-bonds may be present. This patent describes generally broad parameter ranges for the deposition processes. The physical characteristics of the resulting coating layers are thus also ranging between large boundaries. It is not obvious how to select these parameters in view of reaching certain predetermined and interesting properties, such as the production of deposited layers with a very high degree of hardness and/or with a very low coefficient of friction, even in humid air with a relative humidity above 50% or in water or solutions or emulsions in water.